The Digestive System and Body Metabolism Ch 14d

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The Digestive System and Body MetabolismCh 14d
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Metabolic Pathways Involved in Cellular
Respiration

• Glycolysis energizes a glucose molecule so that
  it can be split into two pyruvic acid molecules
  and yield ATP
• In cytoplasm

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Metabolic Pathways Involved in Cellular
Respiration
Figure 14.18
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Metabolic Pathways Involved in Cellular
Respiration

• Krebs cycle
• Produces virtually all the carbon dioxide and
  water resulting from cell respiration
• Yields a small amount of ATP
• In mitochondria

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Metabolic Pathways Involved in Cellular
Respiration

• Electron transport chain
• Hydrogen atoms removed during glycolysis and
  the Krebs cycle are delivered to protein
  carriers

Figure 14.19a
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Metabolic Pathways Involved in Cellular
Respiration

• Electron transport chain (continued)
• Hydrogen is split into hydrogen ions and
  electrons in the mitochondria

Figure 14.19a
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Metabolic Pathways Involved in Cellular
Respiration

• Electron transport chain (continued)
• Electrons give off energy in a series of steps
  to enable the production of ATP
• Also forms H2O

Figure 14.19a
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• Hyperglycemia increased blood glucose excess
  stored in liver as glycogen in body as fat
• Hypoglycemia decreased blood glucose glycogen
  broken down

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Fat Metabolism

• Handled mostly by the liver
• Use some fats to make ATP
• Synthesize lipoproteins, thromboplastin (clotting
  factor), and cholesterol
• Release breakdown products to the blood
• Body cells remove fat and cholesterol to build
  membranes and steroid hormones
• Used for myelin sheaths of neurons

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Use of Fats for ATP Synthesis

• Stored fats energy
• 9 kcal of energy in 1g of fat
• 4 kcal of energy in 1g carbohydrates or proteins
• Fats must first be broken down to acetic acid
• Within mitochondria, acetic acid is completely
  oxidized to produce water, carbon dioxide, and ATP

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• When low glucose, use fat for ATP
• Fat oxidation is fast, but incomplete
• Produces acetoacetic acid and acetones ? acidosis
  or ketosis
• Atkins diet

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Protein Metabolism

• Proteins are conserved by body cells because they
  are used for most cellular structures
• Ingested proteins are broken down to amino acids

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Protein Metabolism

• Cells remove amino acids to build proteins
• Need 20 amino acids 9 are essential (cannot be
  made by body)
• Synthesized proteins are actively transported
  across cell membranes
• Amino acids are used to make ATP only when
  proteins are overabundant or there is a shortage
  of other sources

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Production of ATP from Protein

• Amine groups are removed from proteins as ammonia
• The rest of the protein molecule enters the Krebs
  cycle in mitochondria
• The liver converts harmful ammonia to urea which
  can be eliminated in urine

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Role of the Liver in Metabolism

• Several roles in digestion
• Makes bile
• Detoxifies drugs and alcohol
• Degrades hormones
• Produce cholesterol, blood proteins (albumin and
  clotting proteins), lipoproteins
• Albumin maintains osmotic pressure of blood
  keeps fluids in
• Plays a central role in metabolism
• Process all nutrients

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• Removes amino acids, fatty acids glucose for
  later use
• Remove bacteria
• Die within 24 hours of liver loss
• Have excess liver tissue it also regenerates
• Hepatic portal circulation-
• Brings nutrient-rich blood from digestive system
  to liver so liver can process it

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Metabolic Functions of the Liver

• Glycogenesis
• Glucose molecules are converted to glycogen
• Glycogen molecules are stored in the liver
• Glycogenolysis
• Glucose is released from the liver after
  conversion from glycogen
• Gluconeogenesis
• Glucose is produced from fats and proteins

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Metabolic Functions of the Liver
Figure 14.21
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Metabolic Functions of the Liver

• Fats and fatty acids are picked up by the liver
• Some are oxidized to provide energy for liver
  cells
• The rest are broken down into simpler compounds
  and released into the blood
• Acetic acid acetoacetic acid
• Makes cholesterol

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Cholesterol Metabolism

• Functions of cholesterol
• Serves as a structural basis of steroid hormones
  and vitamin D
• Is a major building block of plasma membranes
• Not used for energy
• In bile salts
• Most cholesterol is produced in the liver (85)
  and is not from diet (15)

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Cholesterol Transport

• Cholesterol and fatty acids cannot freely
  circulate in the bloodstream
• Not water soluble
• They are transported by lipoproteins (made in
  liver) (lipid-protein complexes)
• Low-density lipoproteins (LDLs) transport to body
  cells Bad cholesterol
• High-density lipoproteins (HDLs) transport from
  body cells to the liver good cholesterol

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Body Energy Balance

• Energy intake total energy output (heat work
  energy storage)
• Energy intake is liberated during food oxidation
• Glycolysis, Krebs cycle, electron transport
• Energy output
• Heat is usually about 60 of total
• Storage energy is in the form of fat or glycogen

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Regulation of Food Intake

• Body weight is usually relatively stable
• Energy intake and output remain about equal
• Mechanisms that may regulate food intake
• Levels of nutrients in the blood
• Glucose, amino acids
• Hormones insulin, glucagon, leptin
• Body temperature
• Psychological factors

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Metabolic Rate and Body Heat Production

• Basic metabolic rate (BMR) amount of heat
  produced by the body per unit of time at rest
• energy needed for essential life activities
• Factors that influence BMR
• Surface area small body usually has higher BMR
• Gender males tend to have higher BMR
• 70kg adult has BMR of 60-72 kcal/hr

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Metabolic Rate and Body Heat Production

• Factors that influence BMR (continued)
• Age children and adolescents have a higher BMR
• The amount of thyroxin (from thyroid) produced is
  the most important control factor
• More thyroxin means higher metabolic rate
• Hyperthyroidism- lose weight
• Hypothyroidism- gain weight

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Total Metabolic Rate (TMR)

• Total amount of kilocalories the body must
  consume to fuel ongoing activities
• TMR increases with an increase in body activity
• TMR must equal calories consumed to maintain
  homeostasis and maintain a constant weight
• ? TMR leads to ? weight gain

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Body Temperature Regulation

• Most energy is released as foods are oxidized
• Most energy escapes as heat
• Less than 40 of food energy forms ATP

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Body Temperature Regulation

• The body has a narrow range of homeostatic
  temperature
• Must remain between 35.6 to 37.8C (96 to 100
  F)
• The bodys thermostat is in the hypothalamus
• Initiates heat-loss or heat-promoting mechanisms

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Heat Promoting Mechanisms

• When cold
• Vasoconstriction of blood vessels
• Blood is rerouted to deeper, more vital body
  organs
• Skin becomes cold
• Shivering contraction of muscles produces heat
• Hypothermia
• ? respiration rate, BP, heart rate, metabolism
  comes to a halt

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Heat Loss Mechanisms

• When hot
• Heat loss from the skin via radiation and
  evaporation
• Skin blood vessels and capillaries are flushed
  with warm blood
• Evaporation of perspiration cools the skin
• Less evaporation if humidity is high

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• Hyperthermia
• ? T depresses hypothalamus ? positive feedback
  causing ? metabolism ? ? T ? brain damage
• heat stroke heat loss mechanism NOT working
• Heat exhaustion
• From dehydration ? BP, ? heart rate cool,
  clammy skin, heat loss mechanisms still work

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• Fever
• Body T reset high heat promoting mechanisms
  vasoconstriction, shivering (the chills), ?
  metabolic rate inhibits bacterial growth
• Too high a fever can lead to brain damage

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Body Temperature Regulation
Figure 14.22
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Developmental Aspects of the Digestive System

• The alimentary canal is a continuous tube by the
  fifth week of development
• Digestive glands bud from the mucosa of the
  alimentary tube
• The developing fetus receives all nutrients
  through the placenta
• In newborns, feeding must be frequent (small
  stomach), peristalsis is inefficient, and
  vomiting is common

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• Rooting reflex finding nipple
• Sucking reflex hold nipple and swallow

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• Congenital defects
• Cleft lip/palate
• Tracheoesophageal fistula
• Inborn errors of metabolism
• Cystic fibrosis pancreatic duct blocked
• No fat digestion
• PKU brain damage

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Cleft lip
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Cleft lip
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Cleft lip palate
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Tracheoesophageal fistula
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Developmental Aspects of the Digestive System

• Teething begins around age six months
• Metabolism decreases with old age
• Metabolic rate ? by 5-8/10 years
• Middle age digestive problems
• Ulcers
• Gall bladder problems

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Developmental Aspects of the Digestive System

• Activity of digestive tract in old age
• Fewer digestive juices
• GI activity slows
• Peristalsis slows
• Diverticulosis and cancer (stomach colon) are
  more common